This application is based on Korean Patent Application No. 2003-5361 filed on Jan. 27, 2003, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an optical recording and/or reproducing apparatus, and more particularly, it relates to a defect signal detecting apparatus that detects a defect signal in a signal reproduced from an optical recording medium and accordingly outputs a blank signal, and a defect signal detecting method thereof.
2. Description of the Related Art
Generally, an optical recording and/or reproducing apparatus reproduces data from an optical disc such as a compact disc (CD) or a digital versatile disc (DVD) by emitting a beam of light from a light source such as a laser onto a disc surface and converts the level of the light reflected from the disc surface into an electric signal. The electric signal is called “radio frequency” (RF), and the RF signal is decoded into a binary signal and used for the desired purposes through demodulating process.
Meanwhile, there are usually scratches and dust particles on the surface of the optical disc, and because of their presence, the RF signal may not be always detected at the constant amplitude with respect to the recorded mark. Further, theoretically, the data to be reproduced are arranged in successive order. But in reality, the data may be scattered to different portions of the disc, and in order to read the scattered data, in addition to successive reading in motion from the inner to the outer circumference of the optical disc, the pickup of the optical recording/reproducing apparatus also jumps to a predetermined distance. As a result, there is no output of the RF signal when the pickup is jumping.
Describing the above in greater detail, FIGS. 1A, 1B, 1C and 1D show defects in the reproduced signal, which occurs when: (A) the disc has fingerprints thereon; (B) the pickup jumps to another track during reproducing; (C) the disc has a scratch or a black dot thereon; and (D) the amplitude of the reproduced signal is lower than predetermined first threshold TH1 and predetermined second threshold TH2.
In order to detect the defects likes the ones shown in FIGS. 1A, 1B, 1C and 1D, there is provided a defect signal detecting apparatus for detecting a defect signal, i.e., detecting the abnormal RF signal in the reproduced signal. When the defect signal detecting apparatus detects the defect signal, it outputs a blank signal. The blank signal is then provided to a phase locked loop (PLL) (not shown) or to a binary data decoder, to be used to hold the PLL or temporarily stop the output of binary data.
As shown in FIG. 2, in the conventional defect signal detecting apparatus, the digitized signal output from an A/D converter 10 is input to a maximum value detector 12 and a minimum value detector 14, respectively. The maximum value detector 12 detects an upper value of the incoming RF signals, while the minimum value detector 14 detects a bottom value of the incoming RF signals. A first comparator COMP1 16 compares the upper value with a first threshold TH1, and a second comparator COMP2 18 compares the bottom value with a second threshold TH2. Accordingly, a logic circuit 20 outputs a defect signal according to the results of the comparisons at the first comparator COMP1 16 and the second comparator COMP2 18. That is, if it is determined by the comparison at the first comparator COMP1 16 that the upper value is lower than the first threshold TH1, and by the comparison at the second comparator COMP2 18 that the bottom value is higher than the second threshold TH2, the defect signal is output through the logic circuit 20.
However, the above-mentioned conventional defect signal detecting apparatus detects the normal reproduced signal to be the defect signal when:                (1) the normal reproduced signal is lower than the predetermined first and second thresholds TH1, TH2,        (2) the normal reproduced signal is higher or lower than the predetermined first and second thresholds TH1, TH2 due to deviations occurring in the amplitude of RF signal during the pickup reading according to types of disc, drive or player in use, and        (3) asymmetries are contained in the normal reproduced signal.        
In the above cases, the defect signal detecting apparatus with the fixed thresholds TH1, TH2 detects a defect signal, while it is actually a normal reproduced signal, and accordingly outputs a blank signal.